I am 50 this year, and (within the last five years) have run three half marathons.
I was never, and am not, an uber fit type - this was quite a struggle each time and took over 3 hours.
Anyway, talking to a friend who has just engaged a 'running coach' it seems I can't run properly.
I am 'heel striking' the floor - which is a big no no. (and probably explains why I am not actually any good)
Just tried a short run with using the 'front' part of my feet to land on, and that didn't feel any easier.
You learn something new every day